There is a growing demand for the most accurate possible three-dimensional presentation of the appearance and course of vessels in parts of the body, especially of arteries and veins, for diagnostic purposes in the field of vessel diseases and their treatment. The examination of cerebral aneurysms represents an important area of application, which also includes an analysis and optimum presentation for definition of the aneurysm neck under topographical relationships to adjacent vessels. Angiographies are also performed on other parts of the body in order to identify arteriosclerotic changes or malformations. The introduction of computer-aided rotation angiography, which reconstructs three-dimensional presentations with an even resolution from the raw projection data achieved a technical breakthrough in the field of diagnostics. Prior art in this case are what are known as C-arm-angiographs, in which an x-ray source and a sensor arranged opposite this source are rotated in an approximately 200° arc around the part of a patient's body to be examined and between 50 and 500 x-ray images are recorded and digitally stored during this process. Projection x-ray images recorded from different angles of projection can then be computed into a three-dimensional model of the x-rayed part of the body. However, with conventional 3D angiography it is not possible to make a sufficiently clear distinction between arterial and venous vessel system because of the recording times and the dynamics of the contrast medium propagation.
With the previously known three-dimensional vessel presentation what are known as a masking run and a filling run are recorded. In the masking run the C-arm is rotated around the part of the patient's body or around the entire patient and the x-ray images are recorded over the predetermined angular range. Contrast media is then injected into the vessel of interest and a second set of x-ray images is recorded with a new C-arm rotation, mapping what is known as the filling run. The models of the two sequences of images are now subtracted from one another so that only the contrasted vessels (i.e. those containing contrast media) are still visible in the result. These are now reconstructed using a 3D reconstruction method into a three-dimensional data set. Alternatively masking and filling run can also be reconstructed separately and the resulting three-dimensional data sets subtracted from each other.
The 3D angiography method according to the prior art as a rule delivers a three-dimensional data set which represents both a part of the arterial and also parts of the venous vessel system. The reason for this deficiency of current angiography systems can be found in the fact that the rotation time of the tomograph, at appr. 5 secs, is far longer than what is referred to as the arterial phase of the vessel contrasting, which only lasts 2 to 3 secs. Thereafter the contrast media migrates via the usual capillary paths into the venous vessel system, so that, after the execution of the arterial phase, a venous phase shows the vessel contrasting which will recorded in a later part of the rotation of the tomograph, so that a three-dimensional mixed structure made up of arteries and veins is produced.